1. Field of the Invention
An object of the invention is a mobile device and a method for the management of a standby mode in a mobile device of this kind. The field of application of the invention is preferably that of mobile telephony. However, the invention can also be applied in any other field using integrated circuits and involving several modes of operation, such as for example the field of portable or laptop computers. The aim of the invention is to reduce the amount of space required by the circuits contained in a mobile device as well as their cost price.
2. Description of the Prior Art
At present, one of the main characteristics of mobile telephones is their autonomy in standby mode. This autonomy depends inter alia on the power consumption of the telephone in this mode. When a telephone is in standby mode, a mobile telephone listens to the network in order to find out if whether it is receiving an incoming call. These listening operations take place at points in time or dates planned by the network and communicated by the network to the mobile telephone. Between two consecutive dates, the mobile telephone has but very few or no processing operations to perform. All it has to do is to ensure that it is ready for the next listening operation. It therefore has to measure a period of time.
At present, the modes, whether active or standby, are managed by one and only one very large-scale integrated circuit. This circuit is connected to two quartz crystals, one with a high frequency of typically 13 MHz, and the other with a low frequency of typically 32 KHz. The very large-scale integrated circuit can work at both these frequencies. In the active mode, the very large-scale integrated circuit has many processing operations to perform and is subjected to heavy time constraints. It therefore has its pace set by the 13 MHz quartz crystal. This implies high consumption. In the standby mode, the integrated circuit has few processing operations to perform and the time constraints are relaxed. It therefore switches into a lower-grade mode of operation and has its pace set by the 32 KHz quartz crystal. This has the effect of reducing consumption, for example by the ratio of the frequency of the two quartz crystals. The mobile telephone is in active mode during a listening operation. It is in standby mode between two successive listening operations.
The problem encountered in an embodiment of this kind is related to the nature of the slow oscillator. This slow oscillator is a quartz crystal, namely a block of quartz with a defined shape that is placed between two electrodes. When a voltage is applied to these electrodes, a mechanical deformation of the quartz crystal is obtained. The quartz crystal then goes into oscillation and delivers a signal at the frequency for which the system has been calibrated. For a given frequency, a system of this kind has a minimum space requirement. Consequently, the use of a quartz crystal hampers integration since a quartz crystal of this kind cannot be integrated.
Furthermore, quartz crystals are precision systems. Indeed, it is they that set the pace of the work of the mobile telephone and synchronize it with the network. Making a quartz crystal entails the application of costly technologies to meet demanding specifications, and this increases the total cost of the mobile telephone.
The invention resolves these problems by replacing the quartz crystal with an RC type oscillator delivering a signal with a frequency identical to that of a signal delivered by a quartz crystal. Oscillators of this kind are made with mastered technologies and accept total integration. Thus, a very substantial gain in space is obtained for zero cost. Indeed, the oscillator is integrated into a total integrated circuit and brings only a few transistors into play. A total integrated circuit for its part has several hundreds of thousands of transistors and the addition of these few transistors does not alter its cost.
An object of the invention therefore is a mobile device comprising:
a processor integrated circuit needed to implement the activity of the mobile device,
means to place this device in standby mode and active mode,
two oscillators to set the pace of the processor integrated circuit, a first slow oscillator useful in a standby mode, and a second fast oscillator useful in an active mode,
wherein the slow oscillator is an RC type oscillator.
An object of the invention is also a method for the management of a standby mode of a mobile device wherein:
the device is made to work in active mode by means of a fast oscillator recognized to be stable,
for a standby mode of the device, there is provided a date of activation of the device, this date being stored in a register,
parameters useful for the management of the standby mode are computed, and the parameters are stored in a memory,
the device is placed in standby mode and then the device is repositioned in active mode on the planned date of activation by means of a slow oscillator,
wherein just before a passage into standby mode and regularly during this standby mode:
a slow RC oscillator is calibrated with the fast oscillator,
the result of the calibration is stored in a register,
a duration of inter-calibration is planned,
the slow RC oscillator is calibrated again at the end of the inter-calibration period.